Stereophonic loudspeaker system

ABSTRACT

A STEREOPHONIC LOUDSPEAKER SYSTEM IS PROVIDED COMPRISING TWO PAIRS OF LOUDSPEAKERS. EACH PAIR IS ORIENTED WITH THEIR AXES AT RIGHT ANGLES TO EACH OTHER AND SUBSTANTIALLY EQUIDISTANT FROM THE POINT OF INTERSECTION OF THE AXES. THE SPEAKERS ARE SO ARRANGED THAT ONE SPEAKER OF EACH PAIR FACES THE LISTENER AND THE OTHER SPEAKER HAS ITS AXIS SUBSTANTIALLY PERPENDICULAR TO THE LISTENER. MEANS ARE PROVIDED FOR MATRIXING THE SIGNALS PRODUCED BY A RIGHT AND LEFT AMPLIFIER SYSTEM TO PROVIDE A SUM SIGNAL AND A DIFFERENCE SIGNAL. SUM SIGNALS ARE APPLIED IN PHASE TO THE SPEAKERS WHOSE AXES ARE DIRECTED TOWARD THE LISTENER, AND DIFFERENCE SIGNALS ARE APPLIED TO THE SPEAKERS WHOSE AXES ARE POSITIONED AT RIGHT ANGLES WITH RESPECT TO THE DIRECTION OF THE LISTENER, THE DIFFERENCE SIGNALS TO THE TWO PERPENDICULAR SPEAKERS BEING APPLIED 180* OUT OF PHASE WITH EACH OTHER. AS A RESULT, A STEREOPHONIC SOUND EFFECT IS PRODUCED BY THE SYSTEM.

[72] lnventor James 1?. lilolm 1335 Calhoun, Kalamazoo, Mich. 49007 [21] Appl. No. 747,946 [22} Filed July 26, 1960 [4S] Patented June 20, 11971 [54] STMREOPHONIC LUUDSPEATKEIR SYSTEM 9 Cllnims, 1 Drawing Figs.

[52] US. Cl 179/1, 179/ 1.3 [51] Int. Cl W0 1i 5/02 [50] Field oi rch ..179/1.3, 1.3 (A), 1.3-(PS), 100.1 (TD) [56] Reierences Cited UNITED STATES PATENTS 2,710,662 6/1955 Camras 181/31 3,124,694 3/1964 Pflager etal 179/l(PS) FOREIGN PATENTS 891,014 8/1959 GreatBritain 179/1(PS) Primary Examiner-Kathleen H. Claffy Assistant Examiner-Charles W. Jirauch Attorney--Samuel liurlandsky ABSTRACT: A stereophonic loudspeaker system is provided comprising two pairs of loudspeakers. Each pair is oriented with their axes at right angles to each other and substantially equidistant from the point of intersection of the axes. The speakers are so arranged that one speaker of each pair faces the listener and the other speaker has its axis substantially perpendicular to the listener. Means are provided for matrixing the signals produced by a right and left amplifier system to provide a sum signal and a difference signal. Sum signals are applied in phase to the speakers whose axes are directed toward the listener, and difference signals are applied to the speakers whose axes are positioned at right angles with respect to the direction of the listener, the difference signals to the two perpendicular speakers being applied 180 out of phase with each other. As a result, a stereophonic sound effect is produced by the system.

PATENTED JUN28 I97! SHEET 1 OF 2 MW A m m Q -w WW w 2 6 2 HQ 3 L a we? INVENTOR James R Ha/m PATENTEB JUN28 Ian SHEET 2 BF 2 H m llnlit INVENTOR James P Ho/m VL. rm X a ATTORNE S'lllElklEOlPll-TONIIC LOUIDSIPEAIKER SYSTEM BACKGROUND OF THE INVENTION The present invention relates to systems for the reproduction of stereophonic sound and is more particularly concerned with such a system utilizing signal matrixing and geometrically positioned loudspeakers.

In the reproduction of stereophonic sound, it is common prior art practice to employ signals from two separate channels, a left channel and a right channel, or, as the signals are often referred to, A signal and B signal. In such a system generally each signal is amplified by a separate audio power amplifier, the output signal of each amplifier being introduced to a separate loudspeaker system. The separate loudspeaker systems are generally spaced from 6 to 8 feet or more apart to provide two distinct sources of sound each of which reaches the listener from a different angle to provide a stereophonic effect. Systems of the type described have been found suitable for home and studio use, particularly where there is sufficient room available in which to position the spaced'apart systems and where the rather high cost of the speaker components is not a practical deterent. However, when cost is a relevant factor, and particularly where it would be desirable to confine the speaker system to a relatively small space, the traditional stereophonic speaker systems have been found wanting.

SUMMARY OF THE INVENTlON It is an object of the invention to provide a stereophonic speaker system which can be confined within a relatively small enclosure while still providing the sensation of stereophonic sound to marked degree. It is a further object to provide a system which provides adequate fidelity and freedom from distortion while still utilizing relatively inexpensive speaker components. It is still an additional object to provide a system of the type described which, although it is confined to a small space, provides a stereophonic effect which in some respects is even more pronounced than that of traditional system utiliz' ing spaced-apart individual speaker systems. Additional ob jects and advantages will be apparent to one skilled in the art and still other advantages will become apparent hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS The invention in several of its preferred embodiments is illustrated by the accompanying drawings in which:

FIG. 1 is a perspective view of the speaker system of the present invention with the grille covering removed.

FIG. 2 is a schematic diagram showing the electrical connections to the loudspeakers.

FIG. 3 is a top view of another embodiment of the invention broken away to details of construction; and

FIG. A is a cross-sectional view taken at the line 4-4 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a loudspeaker system according to the invention is shown comprising a support having a frontal wall 1, an upper wall 2, a lower wall 3, and a vertical partition 4. Additionally, although not absolutely required, an acoustic enclosure 5 is provided including the frontal wall ll, end walls 6 and 7 upper and lower walls formed as extension of the upper and lower walls 2 and 3, and a rear cover 8. The particular acoustic enclosure shown is similar to the well-known infinite baffle enclosure and is provided with suitable sound absorbing padding therein, not shown. Mounted at circular openings 9 and 10 are loudspeakers l1 and 12. The vertical partition 4 is provided with two circular openings 13 and 141 at which are mounted loudspeakers 15 and 16, and is positioned substantially perpendicular to the frontal wall 1.

The speakers 11 and 15 must be so mounted in relation to each other that their axes are perpendicular and coplanar with respect to each other, and so that the forward axes of the two speakers, that is, the components of the axes extending from the concave portions of the loudspeakers, intersect at a point substantially equidistant from each speaker. The loudspeakers 12 and 16 are arranged in the same relationship with respect to each other as the loudspeakers l1 and 15.

Stereophonic sound, as it is provided from stereophonic records, tape recorders, multiplex FM, or certain musical instruments is normally provided in two channels, a left channel and a right channel, which may for simplicity be designated as A and B channels. In the common prior art sound systems the signal from each channel is amplified and applied to a separate loudspeaker system, the two systems being positioned in spaced-apart relationship. However, in the loudspeaker system of the present invention, in contrast, the A channel and B channels are not applied per se to individual speaker systems. Instead, the A and B channels are matrixed by suitable means to form sum signals (A+B) and difference signals (A-B). The sum signal is applied to both speakers l1 and 12, that is, the speakers mounted on the rear wall and facing the listener. Difference signals (AB) are applied to both the speakers 15 and lit; mounted on the vertical partition, with the signal applied to the speaker 15 being I out of phase with respect to the signal applied to the speaker 16. As a result of this arrangement, sound reproduction is achieved which has highly unique spacial properties, simulating stereophonic sound derived from two separate spaced-apart speaker systems energized by separate channels.

In order to obtain the desired effect with the present system, several conditions must exist. First, two separate spaced-apart sum speakers must be used, and must be mounted on the frontal wall facing the front of the system. Second, each cooperating pair of speakers 11 and and 12 and 16 must be mounted perpendicular to each other with the axes of each pair substantially in the same plane. Additionally, the forward components of the axes of each pair must intersect at a point. This means that the concave surfaces of the cones of each pair of speakers must be disposed toward each other with the forward components of the axes, that is the portions extending from the concave surfaces of the speaker cones substantially intersecting. Further, to obtain optimum results, the cone of each speaker in a cooperating pair must be substantially equidistant from the point of intersection. In other words, the distance from the axis of each of the frontal or forwardly directed loudspeakers 11 and 12 from the transverse partition should be substantially the same as the distance of the axis of each of loudspeakers 15 and 16 from the frontal support ll. It has been further found that relatively small speakers, as for example those having a cone diameter of about 6 inches can be utilized in the present invention to provide results normally obtainable only with speakers of larger size. In fact, experimental optimum results for certain design parameters have been obtained with speakers having a cone diameter of about 6 inches.

Although various forms of matrixing two signals known in the art may be utilized in the present invention, it has been found particularly advantageous to utilize loudspeakers having dual voice coils. Such speakers are known in the art and are readily available on the commercial market.

FIG. 2 illustrates a schematic electrical diagram utilizing such speakers. As shown, the circuit utilizes two channels, A and B connected to a common line designated by the letter C. The circuit comprises speakers ill and 12 having voice coils 117, 18,19 and 20 connected to produce a sum signal (A+B) in each speaker, and different speakers 15 and 116 having voice coils 21, 22, 23 and 24 connected to produce a difference signal in each speaker. Further, the voice coils of the speaker 16 are so connected that the difference signal produced thereby is l80 out of phase with the difference signal produced by the speaker 15. Additionally a conventional volume control comprising variable resistances 26, 27, 28 and 29 ganged together in proper relationship are utilized to control the relative signal strengths of the A and B channels going to the sum speaker pair and thereby controlling the ratio of acoustical sum to difference signals.

A somewhat modified embodiment is illustrated in FIGS. 3 and 4. Here the structure comprises an upper panel 35, a lower panel 36, a frontal panel 37, and a vertical partition 38. An acoustic enclosure similar to that shown in FIG. 1 is formed by panels comprising, in addition to the upper panel 35, lower panel 36, and frontal panel 37, end panels 39 and 40 and a rear cover panel 41. Circular openings 42 and 43 are provided in the frontal panel 37 over which are mounted loudspeakers 44 and 45. The loudspeakers 44 and 45 are similar to loudspeakers 11 and 12 illustrated in FIG, 1, and should preferably be of the two-voice coil type. A third loudspeaker 46 is mounted in an opening in the vertical partition 38 and may be any type of bidirectional speaker. A preferred type is the well-known electrostatic speaker. The loudspeaker should be designed to radiate equally efficiently in both directions and to be energized by a difference (A-B) signal. This may be accomplished by using a dual voice coil speaker or by other suitable arrangements such as a matrixing network. As in the arrangement shown in FIG. 1, the axis of the speaker 46 should be perpendicular to the axes of the speakers 44 and 45 and should intersect their axes at a point substantially equidistant from the speakers.

In order to finish the appearance of both the embodiment of FIG. 1 and that of FIGS. 3 and 4, a grille cloth may be utilized to cover the front and sides to provide a decorative appearance.

Although a complete theory as to the mode of functioning of the present system has not been developed and it is not desired to be held to any particular theory of operation, conventional measurements and tests of the present system have revealed interesting information from which some inferences may be drawn. When used indoors, the reproduced sound will usually be made up of two components.

A. First component.

For example, with respect to each cooperating pair of speakers mounted at right angles to each other, as for example loudspeakers 11 and 15, or 12 and 16, it has been found that when signals of equal magnitude are applied to the sum speaker 11 and difference speaker 15, the vector product of the sum speaker 11 and difference speaker 15 leaves the system at an angle of 45 to 60 from the forward direction. The signal then strikes a large, adjacent flat reflecting surface such as a wall and is then redirected back across the axis of this system.

B. Second Component.

The second sound component is created in a less direct manner. As a loudspeaker membrane moves through the fluid medium of air, air flows from the forward surface of the speaker to the rear, or following surface, past the edge of the speaker membrane. This air motion is thus in a direction opposite to the motion of the speaker and is a property of any acoustic doublet radiator operating at frequencies with wavelengths greater than one-half the smallest distance across the moving radiator membrane and any associated baffling. This movement of air perpendicular to the difference speakers mounting plane is utilized in conjunction with air movement directly away from the sum speaker pair (this movement being parallel to the mounting plane of the difference speakers) to form a combined air movement consist ing of proportional components of direct and perpendicular air movement. In practical measurements under anechoic chamber and also outdoor conditions, angles of up to 5 across the 0 axis of this system may be obtained by reducing the sum radiation by about 17 db. for full left and right applied stereo signals. This angle was measured by using a figure eight" pattern ribbon microphone as an edgewise null detector, in an anechoic chamber. lt is to be noted that the apparent side of approach of the transverse/direct sound product and the reflection of the simple phase addition wave are the same.

It has been found that the ratio of the sum to difference signal in each cooperating pair of loudspeakers to a large extent determines the proper functioning of the system. When the sum and difference signals are equal, the sound of the system approaches that of two conventional loudspeakers mounted one above the other on the same vertical axis and aimed at an angle of 45 to 60 to each side of center. On the other hand, when the sum signal is reduced the necessary l7 db. for proper outdoor (anechoic) operation and the system is then utilized indoors, the transverse/direct component is too weak to work properly with the strong difference signal reflected from the surrounding walls. Consequently a volume control or attenuator 25 is utilized to balance the sum signals against the difference signals for proper stereophonic effect. This balance control may also be utilized to compensate to a degree for asymmetrical room conditions or for other acoustical environmental situations.

Although the present stereophonic system has been described as suitable for use in the reproduction of stereophonic music from sources such as radios, tape recorders, or phonographs, it is equally well adaptable for use for such types of uses as reproduction from electronic musical instruments.

The stereophonic loudspeaker system of the present invention in its several embodiments illustrated and described have several advantages over conventional stereophonic loudspeaker systems. First, the entire system may be enclosed in a small integral unit and need not be in two spaced-apart sections. In spite of this, the present system is able to produce a stereophonic effect which is quite unique and quite satisfactory for the enjoyment of stereophonic sound. The system utilizes small inexpensive speakers while still providing adequate quality sound. The system is relatively small and inexpensive to manufacture.

It is to be understood that the invention is not limited to the exact details of construction, operation, or exact materials or embodiments shown and described, as obvious modifications and equivalents will be apparent to one skilled in the art, and the invention is therefore to be limited only by the scope of the appended claims.

lclaim:

l. A stereophonic loudspeaker system comprising a support, a pair of forwardly directed spaced-apart loudspeakers mounted on said support in substantially coplanar relationship, a vertical partition mounted on said support and positioned intermediate said forwardly directed loudspeakers, and at least one centrally positioned laterally directed loudspeaker mounted on said vertical partition, each of said forwardly directed loudspeakers having its axis coplanar with and substantially perpendicular to the axis of one of said laterally directed loudspeakers, and means for applying an electrical signal comprising the sum of a pair of stereophonic channel signals to each of said forwardly directed loudspeakers, and means for applying an electrical signal comprising the difference between said pair of stereophonic channel signals to each laterally directed loudspeaker.

2. A stereophonic loudspeaker system according to claim 1, having only one laterally directed loudspeaker arranged to radiate sounds of equal amplitude on both sides of the diaphragm thereof.

3. A stereophonic loudspeaker system according to claim 2, wherein said laterally directed loudspeaker is an electrostatic loudspeaker.

4. A stereophonic loudspeaker system according to claim 1, wherein the means for applying the sum and difference signals comprises two voice coils mounted on each loudspeaker, the voice coils of each forwardly directed loudspeaker being connected in relationship to provide a sum signal and the voice coils of each laterally directed loudspeaker being connected in relationship to provide a difference signal.

5. A stereophonic loudspeaker system according to claim 1, wherein the distance between the axis of each of said forwardly directed loudspeakers to the laterally directed loudspeaker with which it cooperates is substantially the same as the distance between the axis of each of said laterally directed loudspeakers to the forwardly directed loudspeaker with which it cooperates.

6. A stereophonic loudspeaker system comprising frontal support, a pair of forwardly directed laterally spaced-apart loudspeakers mounted on said support in substantially coplanar relationship, a vertical partition perpendicularly mounted on said support and positioned intermediate said forwardly directed loudspeakers, and a pair of vertically spacedapart laterally directed loudspeakers mounted on said vertical partition in substantially coplanar relationship and being oppositely oriented to each other, one of said forwardly directed loudspeakers having its axis coplanar with and substantially perpendicular to the axis of one of said laterally directed loudspeakers and having the forwardly directed portion of its axis intersecting the forwardly directed portion of the axis of said laterally directed loudspeaker, and the other of said forwardly directed loudspeakers having its axis coplanar with and substantially perpendicular to the axis of the other of said laterally directed loudspeakers and having the forwardly directed por tion of its axis intersecting the forwardly directed axis of said laterally directed loudspeaker, means for applying an electrical signal comprising the sum of a pair of stereophonic channel signals to each of said forwardly directed loudspeakers, and means for applying an electrical signal comprising the difference between said pair of stereophonic channel signals to each of said laterally directed loudspeakers, the difference signals being applied to said laterally directed loudspeakers in out-of-phase relationship with respect to each other.

7. A stereophonic loudspeaker system according to claim 6,

wherein the means for applying the sum and difference signals comprises two voice coils mounted on each loudspeaker, the voice coils of each forwardly directed loudspeaker being connected in relationship to provide a sum signal and the voice coils of each laterally directed loudspeaker being connected in relationship to provide a difference signal.

8. A stereophonic loudspeaker system according to claim 6, wherein the distance between the: axis of each of said forwardly directed loudspeakers to the laterally directed loudspeaker with which it cooperates is substantially the same as the distance between the axis of each of said laterally directed loudspeakers to the forwardly directed loudspeaker with which it cooperates.

9. A stereophonic loudspeaker system comprising a support, forwardly directed loudspeaker means mounted on said support, a vertical partition mounted on said support and positioned in a plane passing through the midpoint of said forwardly directed loudspeaker means, and at least one centrally positioned laterally directed loudspeaker mounted on said vertical partition, means for applying an electrical signal comprising the sum of a pair of stereophonic channel signals to said forwardly directed loudspeaker means, and means for applying an electrical signal comprising the difference between said pair of stereophonic channel signals to each laterally directed loudspeaker. 

